1. Field of the Invention
This invention relates to a musical tone synthesizing apparatus used for the synthesis of the musical tones of a plucked-string or struck-string musical instrument or the like.
2. Prior Art
A first type of prior art known is an apparatus which synthesizes the tones of an acoustic musical instrument by means of simulating the tone generation mechanism of an acoustic musical instrument. For example, a construction in which a low pass filter which simulates the reverberation loss of a string and a delay circuit which simulates the propagation delay of the vibration of the string are connected in a closed loop is known. In this type of construction, when an excitation signal such as an impulse or the like is introduced into the closed loop, this excitation signal circulates around the closed loop. In this case, the excitation signal travels once around the closed loop in an amount of time equal to the vibrational cycle of the string, and the frequency band is restricted when the signal passes the low pass filter. Then the signal circulating around the closed loop is extracted and used as a musical tone signal of a stringed instrument.
According to this type of musical tone synthesizing apparatus, by varying the delay period of the delay circuit and the frequency characteristics of the low pass filter, musical tones can be synthesized which are close to those of acoustic stringed instruments which have different tone colors, such as plucked-string instruments (for example, guitars) and struck-string instruments (for example pianos). This type of technique is disclosed In, for example, Japanese Patent Application, Laid-open Number Sho. 63-40199, and U.S. Pat. No. 4,130,043.
In, for example, acoustic musical instruments such as pianos, by means of a hammer striking a string, the string is caused to vibrate at a fixed frequency and a musical tone is generated. In this case, a string and a hammer is provided for each of a plurality of keys. Accordingly, in this type of acoustic musical instrument, there are differences in the position at which the string is struck for each key, and there are slight differences between generated tone colors as a result of difference in striking position. However, in the musical tone synthesizing apparatus introduced above as the first type of prior art, because no account is taken of the corresponding relationship between the delay period in the delay circuit of the closed loop circuit and the key codes corresponding to each key, there is a problem in that it is impossible to cause each key code (each key) to slightly differ in tone color.
In contrast, a second type of prior art known is a musical tone synthesizing apparatus which uses a waveform memory. In this apparatus, a plurality of musical tone data having differing waveform characteristics are stored in advance in a waveform memory; this plurality of musical tone data is synthesized in correspondence with control parameters for changing tone color, Interpolation calculations are carried out between each musical tone data, and musical tones with complex tone colors are thus synthesized.
In this second type of musical tone synthesizing apparatus, complex tone color control can be realized, but as the parameters which cause the differences in tone color in acoustic musical instruments are all mixed, it is impossible to separately control solely the differences in tone color caused by differences in the striking position on the string as discussed above. As a result, in this type of musical tone synthesizing apparatus, there is a problem in that it is impossible to cause slight differences in tone color for each key code (each key).